1. Field of the Invention
The present invention relates to a recirculating-ball nut and screw set with lubricating means, which is suitable for use in industrial robots, semiconductor fabricating equipments, precision instruments, machine tools, and so on.
2. Description of the Prior Art
The linear motion guide units have been conventionally incorporated in the parts or components movable back and forth, which are used extensively in engineering fields as diverse as industrial robots, semiconductor fabricating equipments, inspection instruments, machine tools, and so on. The recently remarkable development in mechatronics technology extensively requires linear motion guide units because of high precision, high speed, compactness and so on. Moreover, the linear motion guide units recently have become required to meet with a need of maintenance-free, along with high precision and high speed in operation. To cope with the maintenance-free demands, the linear motion guide unit has required the self-lubrication of long-lasting service life on its relative sliding areas.
A recirculating-ball nut and screw set for the linear motion guide units shown in FIGS. 14 and 15 is conventionally well known and, for example, as disclosed in Japanese Patent Laid-Open No. 273552/1997. The prior recirculating-ball nut and screw set in FIGS. 14 and 15 is mainly comprised of a screw shaft 1 made around an outer periphery 13 thereof with a helical external groove 3 extending lengthwise of the screw shaft 1, a ball nut 2 fit loosely over the screw shaft 1 and provided on an inner surface 12 thereof with a helical internal groove 14 confronting the helical groove 3 of the screw shaft 1, balls 7 charged to roll in a raceway 15 defined between the confronting helical grooves 3 and 14, and a return guide 4 allowing the balls 7 to recirculate from one end to the other end of the ball nut 2. The ball nut 2 is composed of a flange 6 made with bolt holes 11 to fasten any object such as appliances, bases, parts, components, and so on thereto, and a hollow cylinder 17 having the helical internal groove 14 on the inner surface 12 thereof. The return guide 4 is communicated at its opposite ends to the raceway 15 through connecting port formed in the ball nut 2 and also secured to a flat area 20 on the hollow cylinder 17 of the ball nut 2 by means of a fastener 8, which is held with machine screws 19.
The ball nut 2 has a lubricant supply port 9 threaded at 18, where a lubricant line, not shown, is connected to feed lubricant to the helical grooves 3 and 14 and balls 7. Moreover, the recirculating-ball nut and screw set is provided with either wiper seals 5 or labyrinths. On forward and aft ends of the nut 2 there are annular recesses 16 in which the wiper seals 5 fit, each to each recess, to keep foreign matter such as dust and dirt from invasion inside the nut 2, especially inside the raceway 15.
There are also well known linear motion guide units with onboard lubricant plates, for example as disclosed in Japanese Patent Laid-Open No. 27861/2000, in which a slider with onboard lubricant plates fits over a round track shaft for sliding movement and any lubricant plate may be applicable without any modification on basic design specifications and also installed detachably in the slider. The lubricant plate is usually made of a sintered resinous component of cellular structure, which is impregnated with any lubricant and secured onto a core metal. The sintered resinous component is fabricated by heating finely powdered synthetic resin under pressure in a design mold. Each lubricant plate is held on a carriage of the slider, with interposed between the core metal and an end cap, which are arranged on any one of the forward and aft ends of the slider. Thus, the lubricant plates are allowed to travel relatively to the round track shaft, with keeping sliding engagement with at least raceway grooves on the track shaft.
Another type of the linear motion guide unit is disclosed in Japanese Patent Laid-Open No. 35038/2000, in which the slider with onboard lubricating plate assemblies fits over the round track shaft for sliding movement and installed in a large bore formed in appliance housing. The slider is also kept against escape out of the track shaft by means of retaining rings. The lubricating plate assemblies are each enclosed in a case and composed of a lubricant plate of sintered resinous component having cellular structure impregnated with lubricant, and an end seal. The lubricant will ooze little by little from the lubricant plate to lubricate the round track shaft as the slider moves along the round track shaft.
A recirculating-ball nut and screw set with onboard lubricating means is also known, for example disclosed in Japanese Patent Laid-Open No. 81103/2000, in which lubricant-containing polymer members are mounted on a ball nut, with coming into sliding contact with only the outermost diametral periphery of the round track shaft. When the slider moves along the round track shaft, the lubricant-containing polymer members slide on the round track shaft without scraping away the lubricant deposited in the grooves. Thus, the lubricant always remains accumulated in the grooves where the balls run through there.
In Japanese Patent Laid-Open No. 184683/1998 there is disclosed a linear motion guide unit having incorporated with a lubricant supply means, which includes a lubricant applicator coming into a sliding engagement with a round track shaft to apply the lubricant thereto, a lubricant occlusive body arranged near the lubricant applicator in a casing to store the lubricant while feed the lubricant to the lubricant applicator, and lubricant-metering means to control an amount of lubricant to be transferred to the lubricant applicator from the lubricant occlusive body.
Meanwhile, as the linear motion guide units such as linear rolling motion guide units, recirculating-ball nut and screw set and the like are recently finding a growing variety of applications in diverse fields, they become increasingly used under unfavorable operating conditions or adverse environments, for example, where no replenishment of lubricating oil is allowed, much dirt and debris contamination may occur and there is abnormally high in temperature or moisture. In recent years the linear motion guide units are needed to work in any clean room where the occurrence of dirt and debris has to be staved off to keep the desired cleanliness. Because of the current tendency as stated earlier, much attention has been given the development of the linear motion guide units having no fear of lubrication failures even under the severe operating conditions where it is very hard to achieve the normal lubrication. For the recirculating-ball nut and screw set, especially any maintenance-free lubrication system is needed and so many kinds of the lubrication systems have been heretofore devised to be installed in the recirculating-ball nut and screw set.
Nevertheless, many prior lubrication systems are installed on any one of forward and aft ends of the recirculating-ball nut and screw set, and complicated in construction, very tough to produce them, needed to modify the specification in compliance to the design of the ball nut and screw set to which the lubrication system is applied, and also troublesome to use. Recent advances in the various equipments such as semiconductor fabricating equipments and the like result in the diversity and higher speed of the linear motion guide units. Even if any periodic lubrication were ensured, there would be no possibility of lubrication failure led to any breakage or premature age. However, the piping work for lubrication system is tedious and the current operating situations make it even tougher to ensure that lubricant is supplied evenly into all the sliding surfaces. Thus, it remains a major challenge to develop a recirculating-ball and screw set that is maintenance-free in lubrication and also less in the occurrence of dirt and debris.
With the lubrication system incorporated in the recirculating-ball nut and screw set constructed as stated earlier, for instance a lubricant-containing polymer member is employed, in which a polymer member is mixed with lubricant and fused by heating, followed by solidification in a desired mold under high pressure in cold temperature. The lubricant-containing polymer member stated earlier, because of sophisticated in production technology, need the high technology and expensive cost for the production thereof.
The present invention has for its primary object to resolve the subject matter as stated above, and to provide lubrication means of maintenance-free, which is suitable for a recirculating-ball nut and screw set commonly used to drive a slider in linear motion guide units. More particularly, the present invention provides a recirculating-ball nut and screw set with lubrication means that has a lubricating plate assembly of self-lubrication, which makes it possible to continue keeping the desirable lubrication even under any severe working conditions, thereby making sure of an acceptable long service life and improvement in dustproofing, moreover refraining from the occurrence of dirt and debris to keep a clean environment, and realizing sufficient maintenance-free as for lubricant replenishment, with even easy to produce it. According the lubrication means of the present invention, any presently available linear motion guide unit having a round track shaft may have simply mounted with the lubricating plate assembly with only some modifications on design consideration.
The present invention is concerned with a recirculating-ball nut and screw set with lubrication means, comprising a round screw shaft extending lengthwise, a ball nut fitting around the screw shaft to provide a slider movable along the screw shaft by virtue of balls as the screw shaft turns on its own axis, and lubrication means installed on at least one end of forward and aft ends of the ball nut, wherein the lubrication means is comprised of a holder fastened to the ball nut, and at least one lubricating plate accommodated in the holder in a manner coming into sliding engagement with a helical groove formed around the round screw shaft, the lubricating plate being made of a sintered resinous component of porous structure having cells impregnated with lubricant.
According to one aspect of the present invention, there is disclosed a recirculating-ball nut and screw set in which the lubricating plate has a tongue that extends inwardly from an inside periphery of the lubricating plate to come partially into sliding engagement with the helical groove, so that the lubricating plate makes sliding engagement with the helical groove at only the tongue when the ball nut moves back and forward with respect to the crew shaft.
According to another aspect of the present invention, there is disclosed a recirculating-ball nut and screw set in which the tongue of the lubricating plate is made less in width than the helical groove to thereby making sure of snug fit in the helical groove, while the width of the tongue in the lubricating plate is substantially equal in size with a thickness of the lubricating plate.
According to another aspect of the present invention, there is disclosed a recirculating-ball nut and screw set in which the lubricating plate includes a first annular lubricating plate made with the tongue, and at least one second annular lubricating plate arranged in surface contact with the first lubricating plate so as to replenish the first lubricating plate with the lubricant. Moreover, the second lubricating plate is identical in configuration to the first lubricating plate without the tongue, and more than one second lubricating plate is accommodated in the holder in a manner lying top on another.
According to another aspect of the present invention, there is disclosed a recirculating-ball nut and screw set in which the first lubricating plate is matched in number to that of the helical groove formed around the screw shaft, and the tongues of the first lubricating plates come into sliding engagement with the helical grooves, each to each groove, to apply the lubricant to the helical grooves, respectively. Moreover, the first and second lubricating plates are both cut away from a sintered resinous stock in a configuration of C-shape where a sector is removed circumferentially.
According to a further another aspect of the present invention, there is disclosed a recirculating-ball nut and screw set in which the holder is made in a hollow cylinder having an outside diameter made somewhat smaller than that of the ball nut.
According to another aspect of the present invention, there is disclosed a recirculating-ball nut and screw set in which the holder is fit at any one end of forward and aft ends thereof in the ball nut, while at another end around a wiper seal.
According to another aspect of the present invention, there is disclosed a recirculating-ball nut and screw set in which the holder is composed of a radially reduced neck having the one end that fits in the ball nut and also has an inside diameter to allow the screw shaft to fit loosely in the radially reduced neck, and a radially enlarged body formed integrally with the radially reduced neck and made larger in outer diameter than that of the radially reduced neck to provide a shoulder, which comes into abutment against an associated end surface of the ball nut. In addition, the radially enlarged body includes a major area for accommodating therein the lubricating plate, which is made larger in inside diameter than that of the radially reduced neck, and the another end for fitting around the wiper seal, which has an inside diameter smaller than that of the major area but larger than that of the radially reduced neck.
According to another aspect of the present invention, there is disclosed a recirculating-ball nut and screw set in which a radial offset owing to a difference between the inside diameter of the another end conforming to the wiper seal and the inside diameter of the major area to contain the lubricating plate therein is instrumental in keeping the lubricating plate against escape out of the major area.
According to another aspect of the present invention, there is disclosed a recirculating-ball nut and screw set in which the lubricating plate is made in a configuration where a sector is cut away circumferentially to form a sectorial gap, and the lubricating plate is compressed to reduce circumferentially the sectorial gap to install the lubricating plate across the another end of the radially enlarged body into the major area inside the holder.
The lubrication means for the recirculating-ball nut and screw set of the present invention, as being constructed as stated earlier, is easy in production, simple in construction, ready for handling such as mounting, replacement and so on, compared with the prior lubrication system. Further, the lubrication means of the present invention is commonly applicable to the currently available recirculating-ball nut and screw set without any substantial modification to the basic design considerations of the prior ball nut and screw set. Since only the tongue formed on the lubricating plate comes into the helical groove around the screw shaft, the lubrication means of the present invention succeeds in much reducing any frictional resistance that is encountered when the ball nut moves back and forward in a sliding manner with respect to the screw shaft. Thus, the lubricating plate incorporated in the lubrication means of the present invention makes sure of a continual application of a proper amount of lubricant to the screw shaft without negatively affecting the relative sliding motion between the ball nut and the screw shaft, thereby improving the sliding characteristics. Moreover, as more than one lubricating plate is accommodated in the holder with being superposed upon each other, lubricant is allowed to flow continually to the tongue, thus making sure of the long-lasting, steady lubrication of the helical groove. As the lubricating plates are installed in a cavity having a large inside diameter in the radially enlarged body of the holder, they are kept against escape out of the holder even when the lubricating plate experiences any stroke of the ball nut.
With the recirculating-ball nut and screw set constructed as stated above, the lubricating plate comes into sliding engagement at only a part thereof with the helical groove. This construction has advantage of reducing any frictional resistance that is encountered when the ball nut moves relatively to the screw shaft, thereby making wear less and also reducing the occurrence of dirt, metal cuttings and so on, with even keeping a smooth, continual supply of lubricant from the tongue to the helical groove to eliminate an occurrence of lubrication failure, thus making sure of good lubrication. In addition, the lubricating plate is impregnated with any lubricant selected from lubricating oils of various kinds so as to conform in functional demands to the porous, sintered resinous component. As an alternative, resinous substance of the sintered component for the lubricating plate may be selected to be suited for the lubricant employed. Moreover, the sintered resinous component for the lubricating plate, as superior in workability and ready for modification in design specifications, may be prepared with high accuracy as any part or component most suitable for the recirculating-ball and screw set incorporated in the semiconductor fabricating equipment and precision instruments.
The lubrication means constructed as stated earlier can easily fit, instead of the wiper seal, in most presently available recirculating-ball nut and screw sets with no need of changing their basic specifications. Namely, the lubrication means according to the present invention may be universally adapted to the various types of the recirculating-ball nut and screw sets, which differ, for example, in size of the ball nut incorporated, as long as the screw shaft is identical in standards. Thus, the present invention provides the lubrication means extensive in applicability. Moreover, the lubrication means of this invention may be simply attached to any ball nut of the recirculating-ball nut and screw sets, which have already been incorporated in cutting machine and the like, thereby easily improving the self-lubrication performance of the recirculating-ball nut and screw sets. Thus, the lubrication means of the present invention may be expected to make sure of self-lubrication performance even under too harsh situation for lubrication, thereby keeping the long-lasting good lubrication in the recirculating-ball nut and screw set to realize the maintenance-free as to lubrication.
Other objects and features of the present invention will be more apparent to those skilled in the art on consideration of the accompanying drawings and following specification wherein are disclosed preferred embodiments of the invention with the understanding that such variations, modifications and elimination of parts may be made therein as fall within the scope of the appended claims without departing from the spirit of the invention.